The present invention relates to a fire extinguishing apparatus and method relying upon a non-flammable liquid, such as water for extinguishing fire including Class A and B fires with a mist formed from a relatively small amount of liquid at a relatively low pressure. The fire extinguishing apparatus intended for use in closed areas, such as, for example, in engine rooms, pump rooms, machinery spaces, computer rooms, storage rooms and the like. More particularly, the present invention relates to a fire extinguishing apparatus intended for use as a replacement for an existing fire extinguishing apparatus based upon the use of the now banned HALON.
Hereinafter, the present invention will be described with particular reference to use with liquid being water although it could be used with other non-flammable liquids which absorb heat as they vaporise.
In fighting fires it is known that there are three major contributing factors to the continuation of the fire. These factors are heat, oxygen and fuel and the interrelationship of these factors is shown pictorially in FIG. 6. Conventionally when extinguishing fires, fire fighters act to remove at least one of the three elements necessary for combustion. Typically, fire fighters use either water, CO2, halon, dry chemical or foam. Water acts by removing the heat from the fuel, whilst carbon dioxide works by displacing the oxygen.
Another aspect of combustion is a chain flame reaction indicated by a circle which contains the triangle, as shown in FIG. 6. The chain flame reaction relies upon free radicals which are created in the combustion process and are essential for of its continuation. Halon operates by attaching itself to the free radicals and thus preventing further combustion by interrupting the flame chain reaction.
The main disadvantage of water is that considerable amounts of water are required in extinguishing a fire which leads to considerable damage by the water. Also, in some instances suitable quantities of water to extinguish the fire are not available. Carbon dioxide and halon both have the disadvantage that all people must be evacuated from the area in which they are to be used must be evacuated since it will become impossible for the people to breathe. For this reason, fire fighters using these extinguishing agents must use breathing apparatus. Also, for CO2 and Halon to extinguish the fire any ventilation of the area must be shut down. Halon has further disadvantage that it is highly toxic and very damaging to the environment. For those reasons, the use of halon in extinguishing fires has been banned in most circumstances.
The present invention overcomes the above disadvantages by using a non-flammable liquid, such as water, to reduce the heat of the vapour around the fuel, reduce the heat of the fuel, displace the oxygen, and interrupt the flame chain reaction. That is, the liquid attacks all parts of the combustion process except for removing the fuel. The invention is based upon the generation of a relatively fine mist of liquid (referred as a mist), such as water, which displaces the oxygen, and upon heating evaporates and expands to further displace the oxygen. Upon expansion the water mist absorbs heat from the vapour around the fuel and from the fuel. Also, the mist interrupts the flame chain reaction by attaching to the free radicals. The mist also has a smothering effect and a cooling effect upon the fire. For these reasons, the mist has the surprising result that a relatively small amount of water can safely be used to extinguish both A and B class fires as well as electrical fires.
The mist generated by the fire extinguishing apparatus of the present invention is not a water on flame scenario. Its operation is more akin to gaseous fire extinguishing mediums such as CO2 or halon.
These surprising results occur due to the very rapid evaporation rate possible with a fine mist of liquid (typically 50-500 microns), the heat absorption characteristics of water as it vaporises, the ability of the fine mist to reduce the convection of heat from the fire to surrounding objects and the ability of the mist to displace oxygen. This is due to the expansion ratio of water from liquid to vapour.
With the fire extinguishing apparatus of the present invention a typical fire confined to a room or the like can be entirely extinguished within about 30 seconds with a number of nozzles each spraying about 0.4 litres of water as mist at about 20 bar, with one nozzle per 2.65 m3. This is a very small rate of application of water to douse a fire when compared to the prior art.
Therefore, it is an object of the present invention to provide a fire extinguishing apparatus which uses a mist generated from non-flammable liquid applied in relatively small volumes to interrupt the combustion process of a fire in a closed space.
In accordance with one aspect of the present invention there is provided a fire extinguishing apparatus for extinguishing a fire located in a risk area, the fire extinguishing apparatus comprising:
a storage reservoir containing a non-flammable liquid;
a spray means for spraying the liquid into the risk area, the spray means forming a mist having a droplet size which enhances the application of the mist to the fire and hence increase the ability for the liquid to extinguish the fire;
a propelling means for propelling the liquid out of the storage reservoir and through the spray means under pressure for forming the mist;
a sensor means for detecting the presence of a fire in the risk area;
a control means in operative association with the sensor means for controlling the propelling means for propelling the liquid out of the storage reservoir.
In accordance with another aspect of the present invention there is provided a method for extinguishing a fire, the method comprising the steps of:
directing a spray means into the risk area;
propelling non-flammable liquid through the spray means under pressure for forming a mist having a droplet size which creates an atmosphere that will not support combustion.
Typically, the non-flammable liquid is water.
Preferably, the spray means includes a plurality of nozzles interconnected by pipes.
Preferably, the mist has a droplet size with a median volume diameter or less than about 500 microns.
Typically, the propelling means is a gas contained in the storage reservoir under elevated pressure. Typically, the gas is dry nitrogen. Typically, the gas is pressurised to about 20 bar in the storage reservoir prior to operation of the fire extinguishing apparatus.